Rotary cutters are employed to cut material passing through extrusion dyes into pellets. For high volume production, one rotary cutter assembly cuts material passing through a number of extrusion passages simultaneously.
Helical cutter blades are preferred to reduce noise, lower vibration and reduce peak loads on the power source. However, helical blades are difficult to manufacture and to sharpen. If the material being cut is relatively rigid, there can be some space between the cutting edges on a driven rotor and the extrusion dye. However, if the material to be cut is somewhat soft, the space between a cutting edge and a dye port must be reduced to near zero to obtain a clean cut.
A rotor for cutting that is currently in use has a plurality of slots that extend the length of the rotor. Each slot extends from one end to the other of the rotor at a slight angle relative to the axis of rotation to provide a helix angle. Each slot also has a cutter blade base support surface that is in a flat plane extending the length of the rotor. A straight blade is supported on the base support. Due to an hourglass effect, the rotor radius extending from the axis of the rotor to the cutting edge of the blade is substantially larger at both ends of the rotor than it is in the center of the blade. To correct for the hourglass effect a plurality of cutter segments are mounted on each base support. The width, in a radial direction, of each cutter segment is varied to correct for the hourglass effect.
The cutter blades are made from special cutter blade materials. These materials are difficult to shape and sharpen. To form a cutting edge on all the cutter blade segments that are within the required range of accuracy it is necessary to mount a complete set of blades on a rotor, mount the rotor in a machine tool and grind the cutting edges to the required shape and dimensions. A rotary cutter with blade segments that have to be ground after the segments are mounted on the rotor is not repairable in the field. If one blade is damaged it is often necessary to remove the rotor from the machine and send it to the manufacturer for repair or blade sharpening.